A series of 11 novel 3‐aryl‐2‐phenyl‐2,3‐dihydro‐4H‐1,3‐benzothiazin‐4‐ones was prepared at room temperature by T3P‐mediated cyclization of N‐aryl‐C‐phenyl imines with thiosalicylic acid. This provides simple and ready access to N‐aryl compounds in this family, which have been generally difficult to prepare.
The crystal structures of isomeric rac-2-(4-nitrophenyl)-3-phenyl-2,3,5,6-tetrahydro-4H-1,3-thiazin-4-one (C16H14N2O3S) (1) and (2S)-2-(3-nitrophenyl)-3-phenyl-2,3,5,6-tetrahydro-4H-1,3-thiazin-4-one (C16H14N2O3S) (2) are reported here. While 1 crystallizes in a centrosymmetric space group, the crystal of 2 chosen for data collection has molecules only with (2S) chirality. This is the result of spontaneous resolution during crystallization, as the synthesis produces a racemic mixture. A crystal with (2R) molecules was also found in the same crystallization vial (structure factors available). The six-membered thiazine ring in both 1 and 2 displays an envelope conformation with the S atom forming the flap. The aryl rings in both structures adopt an approximate V shape with angles between their planes of 46.97 (14)° in 1 and 58.37 (10)° in 2. In both structures, the molecules form layers in the ab plane. Within such a layer in 1, one of the O atoms of the nitrophenyl group accepts a C—H...O hydrogen bond from the CH group at position 5 of the thiazine ring of a molecule of opposite chirality, forming chains along the a-axis direction. Each of the thiazine rings also participate in C—H...O bonds with the same carbon atom as above, resulting in chains along the b-axis direction, albeit of monochiral type. Adjacent layers are consolidated along the c-axis direction by pairs of parallel hydrogen bonds (C—H...O type) between the nitrophenyl groups of enantiomers. In 2, the two C—H...O hydrogen bonds contribute to chain formation along the b-axis direction. Weak edge-to-face interactions between the aryl groups of neighbouring molecules in 1, and C—H...π interactions between a thiazine ring CH group and a phenyl group of a neighboring molecule in 2 are also observed.
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